package com.example.springbootlearn.concurrent;

import java.io.Serializable;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * 实现不可冲入独占锁
 * 我们定义state为0是锁没有线程持有，为1表示锁已经被某以线程持有
 *
 * @author caiji Mr. Li
 * @date 2019/10/23 16:07
 */
public class NonReentranLock implements Lock, Serializable {

    private static class Sync extends AbstractQueuedSynchronizer {
        @Override
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }

        @Override
        protected boolean tryAcquire(int acquire) {
            //修改state为1
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        @Override
        protected boolean tryRelease(int arg) {
            if(getState()==0){
                throw new IllegalMonitorStateException();
            }
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        Condition newCondition() {
            return new ConditionObject();
        }
    }

    private final Sync sync = new Sync();

    @Override
    public void lock() {
        sync.acquire(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }

    @Override
    public boolean tryLock(long timeOut, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireSharedNanos(1, unit.toNanos(timeOut));
    }

    @Override
    public void unlock() {
        sync.release(1);
    }

    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }
}
